An evaluation method for the crack sensitivity of laser cladding

Abstract

The present invention discloses a method for evaluating the crack sensitivity of laser cladding. In this method, a slit is cut starting from the mid-axis at one end of a test plate. After cleaning the surface of the slit, at the end of the test plate where the slit is cut, a U-shaped restraint plate is symmetrically welded on both sides of the slit. A laser is used to perform laser cladding on the metal powder along the slit to form a continuous cladding layer. The crack length on the surface of the cladding layer and the total length of the cladding layer are measured, and the crack rate is calculated. According to the magnitude of the crack rate, the crack sensitivity evaluation of the same type of test plates under different types of metal powders or different types of test plates under the same type of metal powder is completed. The method of the present invention is simple, the crack rate is easy to calculate, the cost is low, the test results are true and reliable, and it is of great significance for the evaluation of the crack sensitivity of laser cladding, the formulation of laser cladding process specifications, the design and optimization of the cladding layer composition, and the development of high crack-resistant cladding materials.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the crack sensitivity of laser cladding, belonging to the technical field of laser cladding. Technical Background

[0002] Laser cladding is a laser-based additive manufacturing technology that can locally process alloys with a small heat input and deformation rate, and has significant advantages in the forming of metal parts and the repair of metal components. It has become a current popular research field. Among its various applications, laser cladding of nickel-based superalloys for aeroengine impeller blades has always been a research focus. Nickel-based superalloys have good high-temperature strength, fatigue performance, oxidation resistance, and corrosion resistance, and are widely used in components such as turbine blades and turbine disks of aeroengines. However, cracks often occur during the laser cladding process of nickel-based superalloys. Therefore, carrying out research on the evaluation of crack sensitivity of laser cladding can, on the one hand, guide the formulation of laser cladding processes, and on the other hand, also have important reference value for the development of high-performance crack-resistant cladding materials.

[0003] There are many existing crack sensitivity testing methods, but most of them are applied to the fields of welding and casting, and there are few for the field of laser cladding. Compared with welding, the cooling rate of laser cladding is large, and specimens are more likely to generate cracks under a large cooling rate. According to the different ways of generating restraint, crack sensitivity tests can be divided into two categories: self-restraint and externally applied restraint. The fishbone-shaped crack test in the form of surfacing is one of the most widely used crack tests, and the crack length generated under the action of self-restraint can be used as an index to evaluate the crack sensitivity of materials. However, in laser cladding tests, due to the small restraint strength generated by fishbone-shaped specimens, even for high crack sensitivity materials, it is difficult to ensure the generation of cracks when using fishbone-shaped specimens, and it is not sufficient to distinguish the crack sensitivity of different materials during laser cladding, and it is difficult to achieve the effect of evaluating crack sensitivity.

[0004] CN112432862 discloses a comprehensive evaluation method for the sensitivity of welding hot cracks. In this method, a square specimen is placed on the sample table of an adjustable restraint testing machine, spot welding is carried out at the center of the specimen, and the specimen is immediately pressed down for bending after the arc is extinguished, and the crack morphology near the weld seam and the fusion line is observed through an optical microscope. The crack sensitivity is evaluated by establishing the corresponding relationships between strain and the number of cracks, the total crack length, etc. However, the welding form of this technology is spot welding, which is difficult to apply to the continuous laser cladding form.

[0005] Yan Shiyong et al. (Crack Sensitivity and Evaluation Method of Ni-based Alloy Laser Cladding Layer [D]. Qingdao: China University of Petroleum (East China), 2016) designed a thin plate free deformation test to evaluate the crack sensitivity of laser cladding. In this method, one end of the test piece is fixed on the fixture, and the rest is in a free state and can deform freely. Cladding is carried out along the length direction from the center of the test piece. After cladding, a vernier caliper is used to measure the deformation of the test piece to evaluate the crack sensitivity of the cladding layer. However, this technology is only applicable to thin plate tests. In actual production, thick plate cladding is mainly used, and it is difficult to evaluate the crack sensitivity during thick plate cladding. In addition, no cracks are generated in this method, but the deformation of the test plate is used to evaluate the crack sensitivity. Since the generation of cracks is not only related to strain but also affected by factors such as material solidification characteristics and composition, relying solely on the deformation of the test plate cannot accurately and comprehensively evaluate the crack sensitivity of laser cladding. Summary of the Invention

[0006] Object of the Invention: Aiming at the deficiencies of the above-mentioned existing technologies, the object of the present invention is to provide an evaluation method for the crack sensitivity of laser cladding.

[0007] Technical Solution: The evaluation method for the crack sensitivity of laser cladding according to the present invention includes the following steps:

[0008] (1) Cut a test plate, start cutting a slit at the mid-axis of one end of the test plate, and clean the surface of the slit;

[0009] (2) At one end of the test plate where the slit is cut, symmetrically weld the U-shaped restraint plate on both sides of the slit;

[0010] (3) Use a laser to perform laser cladding on the metal powder along the slit to form a continuous cladding layer;

[0011] (4) Measure the crack length (L C ) and the total length (L S ) of the cladding layer, and calculate the crack rate (δ);

[0012] (5) Complete the crack sensitivity evaluation according to the size of the crack rate.

[0013] Among them, in step (1), the shape of the test plate is rectangular.

[0014] Among them, in step (1), the test plate includes materials such as nickel-based superalloy, aluminum alloy, titanium alloy, zirconium alloy, high-entropy alloy, magnesium alloy, and steel.

[0015] Among them, steel includes stainless steel, carbon steel, alloy steel, etc.

[0016] Among them, in step (1), the width (W B ) of the test plate is 40 - 80 mm, and the length (LB ) is 3 to 5 times the width, and the thickness (D) of the test plate is 3 to 20 mm.

[0017] Among them, in step (1), the length (L G ) of the gap is 0.5 to 0.6 times the length of the test plate, and the width (W G ) of the gap is 0.5 to 1 mm.

[0018] Among them, in step (2), the cleaning is carried out with acetone or alcohol.

[0019] Among them, in step (2), the U-shaped restraint plate has the same thickness as the test plate.

[0020] Among them, in step (2), the length (L T ) of the bottom of the U-shaped restraint plate is 0.2 to 0.4 times the length (L B ) of the test plate.

[0021] Among them, in step (2), the width (W T ) of the side wall of the U-shaped restraint plate is 0.2 to 0.4 times the width (W B ) of the test plate.

[0022] Among them, in step (2), the length (L R ) of the U-shaped restraint plate is 0.4 to 0.8 times the length (L B ) of the test plate, and the width (W R ) of the U-shaped restraint plate is 0.5 to 1 times the width (W B ) of the test plate.

[0023] Among them, in step (2), the U-shaped restraint plate is symmetrically welded on both sides of the starting point of the gap.

[0024] Among them, in step (2), in order to avoid cracks in the U-shaped restraint plate caused by stress concentration during the cladding process, a chamfer is provided at the inflection point of the U-shaped restraint plate.

[0025] Among them, the diameter of the chamfer is 2 to 3 mm.

[0026] Among them, in step (2), in order to ensure the restraint degree, the U-shaped restraint plate is welded by tungsten inert gas welding, gas metal arc welding or shielded metal arc welding.

[0027] Among them, in step (2), the welding sequence is to weld the cladding side first and then the non-cladding side.

[0028] Among them, in step (3), the metal powder includes nickel-based alloy powder, iron-based alloy powder, cobalt-based alloy powder, high-entropy alloy powder, titanium-based alloy powder, stainless steel alloy powder, etc.

[0029] Among them, in step (3), the laser cladding starts from the starting end of the gap and clads along the gap, and the cladding length is 0.5 to 1.5 times the length of the gap.

[0030] Among them, in step (3), the form of the laser cladding is single-pass cladding.

[0031] Among them, in step (3), the shielding gas used in the laser cladding process is argon or helium with a purity of 99.99%, the flow rate of the shielding gas is 15 to 20 L / min, and the shielding gas is supplied for 10 s before and after cladding.

[0032] Among them, in step (3), to ensure good formation of the cladding layer, the power of the laser during laser cladding is 1 to 3 kW, the scanning speed is 3 to 5 mm / s, and the rate of supplying metal powder is 10 to 30 g / min.

[0033] Among them, in step (4), the calculation of the crack rate (δ) adopts the following formula:

[0034] Crack rate (δ) = crack length (L C ) / total length of the cladding layer (L S ).

[0035] Among them, in step (5), the crack sensitivity evaluation is as follows: According to the size of the crack rate, the crack sensitivity of the same type of test plate under different metal powder types or different types of test plates under the same metal powder type is evaluated. The higher the crack rate, the higher the crack sensitivity of the laser cladding of the test plate or metal powder under this condition. That is, compare the crack rates of the test plates or metal powders and sort them. The higher the crack rate of the test plate or metal powder, the greater the crack sensitivity (for example, when the crack rate sorting of three materials A, B, and C is δ A >δ B >δ C , it indicates that the crack sensitivity of the laser cladding of the materials under this test condition is A>B>C).

[0036] The present invention uses a rectangular test plate with a gap, applies restraint with a flexibly adjustable U-shaped restraint plate, and by adjusting the size of the U-shaped restraint plate (for example, when the size of the test plate is large, by increasing L R , L T and W TTo increase the degree of restraint), laser cladding tests with various process specifications can be carried out. At the beginning of laser cladding, the restraint of the test plate is large, ensuring the generation of cracks. As the cladding progresses, the cracks continue to expand, but along the cladding direction, the restraint of the test plate gradually decreases. When the degree of restraint decreases to the critical value, the crack stops expanding. Through the measured crack rate, under certain cladding process parameters and powder types, the laser cladding crack sensitivity of different test plates of the same powder type or the same test plate of different powder types is evaluated.

[0037] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0038] The method of the present invention is simple, the crack rate (δ) is easy to calculate, the cost is low, and the test results are true and reliable, which is of great significance for the evaluation of laser cladding crack sensitivity, the formulation of laser cladding process specifications, the design and optimization of the cladding layer composition, and the development of high crack resistance cladding materials. Description of the drawings

[0039] Figure 1 Schematic diagram of the specimen after applying restraint in Example 1;

[0040] Figure 2 Schematic diagram of the laser cladding test in Example 1;

[0041] Figure 3 Test result diagram of the crack sensitivity of different cladding powder materials in Example 1;

[0042] Figure 4 Test result diagram of the crack sensitivity of different test plates in Example 2;

[0043] Figure 5 Test result diagram of the crack sensitivity of different test plates in Example 3. Detailed implementation manners

[0044] The technical solution of the present invention will be further described below with reference to the drawings.

[0045] Example 1

[0046] In this example, Inconel 718 nickel-based superalloy material is used as the cladding plate to evaluate the crack sensitivity of different cladding powders:

[0047] (1) Preparation of test plates: Cut a rectangular Inconel 718 nickel-based superalloy test plate 1 by wire cutting. The length L of the rectangular test plate 1 B is 120 mm, the width W B is 40 mm, the thickness D is 3 mm, and the quantity is 12 pieces. Starting from the mid-axis of one end edge of the test plate 1, use a wire cutting machine to cut a line with a length L G of 60 mm and a width WG a gap of 0.5 mm.

[0048] (2) Specimen cleaning: Before laser cladding, the specimen 1 was cleaned with acetone solution to remove the oil stains and scale on the surface of the specimen 1.

[0049] (3) Application of restraint: The U-shaped restraint plate 2 was symmetrically welded on both sides of the starting end of the gap by tungsten inert gas welding. Among them, the dimensions of the U-shaped restraint plate are as follows: the length L of the U-shaped restraint plate R is 48 mm, the width W R is 20 mm, the bottom length L of the U-shaped restraint plate T is 24 mm, the side wall width W of the U-shaped restraint plate T is 8 mm, as Figure 1 shown, Figure 1 is the schematic diagram of the specimen after applying restraint in Example 1.

[0050] (4) Conducting cladding test: Laser cladding was carried out using the laser process, as Figure 2 shown, Figure 2 is the schematic diagram of the laser cladding test in Example 1. At the beginning of cladding, argon with a purity of 99.99% was used as the shielding gas, and the argon flow rate was 15 L / min. Argon was supplied for 10 s before and after cladding. The power of the laser was set to 1 kW, and a laser focusing spot with a spot size of 5 mm×5 mm was placed at the starting point of the gap. Under the action of laser heat, the alloy powder was melted and evenly coated on the surface of the gap. The rate of supplying metal powder was 10 g / min. Then, the laser was moved along the central axis of the specimen 1 from the starting end to the ending end of the gap at a scanning speed of 5 mm / s, and cladding was stopped after cladding 0.5L G length, thus forming a continuous cladding layer. During the cladding process, cracks generated on the cladding layer propagated, and the propagation of the cracks stopped when the restraint degree decreased to a certain extent. The cladding powders were divided into four groups, and the alloy powders in each group were Ni60A, Ni60A + 15%WC, Ni60A + 25%WC, and Ni60A + 35%WC respectively. Each group of tests was repeated three times.

[0051] (5) Calculation of crack rate and sensitivity evaluation: After cladding, the crack length L C was measured. For each group, it was determined by the average crack length of 3 specimens. The measured crack length L C was divided by the total length L S of the cladding layer to obtain the crack rate δ. The crack rates δ obtained by Ni60A, Ni60A + 15%WC, Ni60A + 25%WC, and Ni60A + 35%WC cladding powders were 0.15, 0.28, 0.57, and 0.75 respectively. The results are as Figure 3 shown, Figure 3 is the crack rate diagram of different laser cladding powders. From Figure 3It can be seen that with the increase of WC content, the crack sensitivity of the cladding powder increases. This is mainly because the increase in WC content leads to an increase in the number of hard phases formed in the cladding layer, making it difficult to coordinate strain. While improving the hardness and wear resistance of the cladding layer, it increases the cracking tendency of the cladding layer, resulting in an increase in crack sensitivity.

[0052] The crack rate ranking of the four cladding powders is as Figure 3 shown. The higher the crack rate, the higher the crack sensitivity of the cladding powder. Therefore, the crack sensitivity of the cladding powder materials obtained from the experiment is Ni60A < Ni60A + 15% WC < Ni60A + 25% WC < Ni60A + 35% WC, achieving an accurate and effective evaluation of the crack sensitivity of different cladding powder materials.

[0053] Example 2

[0054] In this example, Ni45 powder is used as the cladding material, and a laser cladding crack sensitivity evaluation experiment is carried out on different stainless steel test plates to evaluate the crack sensitivity of different stainless steel test plates:

[0055] The experimental process is the same as that in Example 1

[0056] (1) Test plate preparation: A rectangular stainless steel test plate 1 is cut by wire cutting. The length L B of the rectangular test plate 1 is 240 mm, the width W B is 80 mm, the thickness D is 20 mm, and the number is 9 pieces. Starting from the mid-axis of one end edge of the test plate 1, a slit with a length L G of 144 mm and a width W G of 1 mm is cut by wire cutting.

[0057] (2) Test plate cleaning: Before laser cladding, the test plate 1 is cleaned with acetone solution to remove the oil and scale on the surface of the test plate 1.

[0058] (3) Application of restraint: The U-shaped restraint plate 2 is symmetrically welded on both sides of the starting end of the slit by gas metal arc welding. The dimensions of the U-shaped restraint plate are as follows: The length L R of the U-shaped restraint plate is 192 mm, the width W R is 80 mm, the bottom length L T of the U-shaped restraint plate is 96 mm, and the side wall width W T of the U-shaped restraint plate is 32 mm.

[0059] (4) Cladding test procedure: Laser cladding process was adopted. At the beginning of cladding, argon gas with a purity of 99.99% was used as the shielding gas, and the flow rate of argon gas was 20 L / min. Argon gas was supplied for 10 s before and after cladding. The power of the laser was set at 3 kW, and a laser focused spot with a size of 5 mm × 5 mm was placed at the starting point of the gap. Under the action of laser heat, the alloy powder was melted and evenly coated on the surface of the gap. The cladding powder material was Ni45, and the feeding rate of Ni45 powder was 30 g / min. Then, the laser was moved along the central axis of test plate 1 from the starting end to the ending end of the gap at a scanning speed of 3 mm / s, and 1.5 L of cladding was carried out along the gap G After the cladding length, the cladding was stopped, thus forming a continuous cladding layer. During the cladding process, cracks generated on the cladding layer would expand, and the crack expansion would stop when the restraint degree decreased to a certain extent. The cladding was divided into three groups, and the stainless steel types of each group were 304 stainless steel, 316 stainless steel, and 310 stainless steel respectively. Each group of tests was repeated three times.

[0060] (5) Crack rate calculation and sensitivity evaluation: After cladding, the crack length L C was measured. For each group, it was determined by the average crack length of 3 specimens. The measured crack length L C was divided by the total length L S of the cladding layer to obtain the crack rate δ. The crack rates obtained for the 304 stainless steel, 316 stainless steel, and 310 stainless steel test plates were 0.14, 0.24, and 0.67 respectively.

[0061] The crack rate ranking of stainless steels with different materials is as Figure 4 shown. Figure 4 It is the crack sensitivity test result diagram of different test plates in Example 2. As can be seen from Figure 4 it, the higher the crack rate, the higher the crack sensitivity of the material. Therefore, the laser cladding crack sensitivities of the test plate materials obtained from the test are 304 stainless steel < 316 stainless steel < 310 stainless steel, which is consistent with the order of stainless steel welding crack sensitivity, achieving an accurate and effective evaluation of the laser cladding crack sensitivities of different materials.

[0062] Example 3

[0063] In this example, Ni60A powder was used as the cladding material, and a laser cladding crack sensitivity evaluation test was carried out on test plates of different material types to evaluate the crack sensitivities of different types of materials:

[0064] The experimental process was the same as that in Example 1

[0065] (1) Test plate preparation: Rectangular Q235 stainless steel, Inconel718, and 430 stainless steel test plates 1 were cut by wire cutting. The length L B of the rectangular test plate 1 was 180 mm, and the width WB is 60 mm, the thickness D is 15 mm, the quantity is 9 pieces. Starting from the mid-axis of one end edge of the test plate 1, a length L is cut with a wire cutting machine G is 100 mm, the width W G is a gap of 0.8 mm.

[0066] (2) Cleaning of the test plate: Before laser cladding, the test plate 1 is cleaned with acetone solution to remove the oil and scale on the surface of the test plate 1.

[0067] (3) Application of restraint: The U-shaped restraint plate 2 is symmetrically welded on both sides of the starting end of the gap by shielded metal arc welding. The dimensions of the U-shaped restraint plate are as follows: The length L of the U-shaped restraint plate R is 90 mm, the width W R is 48 mm, the bottom length L of the U-shaped restraint plate T is 48 mm, the side wall width W of the U-shaped restraint plate T is 18 mm.

[0068] (4) Conducting of the cladding test: Laser cladding is adopted. At the beginning of cladding, argon with a purity of 99.99% is used as the shielding gas, and the flow rate of argon is 18 L / min. Argon is supplied for 10 s before and after cladding. The power of the laser is set to 2 kW, and a laser focusing spot with a spot size of 5 mm×5 mm is placed at the starting point of the gap. Under the action of laser heat, the alloy powder is melted and evenly coated on the surface of the gap. The cladding powder material is Ni60A, and the feeding rate of Ni60A powder is 20 g / min. Then, the laser moves along the mid-axis of the test plate 1 from the starting end to the ending end of the gap at a scanning speed of 4 mm / s until the laser reaches the ending end of the specimen gap and stops cladding, thus forming a continuous cladding layer. During the cladding process, cracks generated on the cladding layer expand, and the crack expansion stops when the restraint degree drops to a certain level. The cladding is divided into three groups, and the test plate types of each group are Q235 stainless steel, Inconel718, and 430 stainless steel respectively. Each group of tests is repeated three times.

[0069] (5) Calculation of crack rate and sensitivity evaluation: After cladding, the crack length L C is measured. For each group, it is determined by the average crack length of 3 specimens. The measured crack length L C is divided by the total length L S of the cladding layer to obtain the crack rate δ. The crack rates obtained for the Q235 stainless steel, Inconel718, and 430 stainless steel test plates are 0.17, 0.31, and 0.69 respectively.

[0070] The crack rate ranking of different materials is as Figure 5 shown, Figure 5 is the crack sensitivity test result diagram of different test plates in Example 3. From Figure 5It can be seen that the higher the crack rate, the higher the crack sensitivity of the material. Therefore, the laser cladding crack sensitivities of the test plate materials obtained from the experiments are as follows: Q235 stainless steel < 430 stainless steel < Inconel 718, which is consistent with the order of the welding crack sensitivities of the three materials, achieving an accurate and effective evaluation of the laser cladding crack sensitivities of different materials.

Claims

1. An evaluation method for the crack sensitivity of laser cladding, characterized in that, It includes the following steps: (1) Cut a test plate, start cutting a slit at the mid-axis of one end of the test plate, and clean the surface of the slit; (2) At the end of the test plate where the slit is cut, symmetrically weld the U-shaped restraint plate on both sides of the slit; the length of the bottom of the U-shaped restraint plate is 0.2 - 0.4 times the length of the test plate, the width of the side wall of the U-shaped restraint plate is 0.2 - 0.4 times the width of the test plate, the length of the U-shaped restraint plate is 0.4 - 0.8 times the length of the test plate, the width of the U-shaped restraint plate is 0.5 - 1 times the width of the test plate, the U-shaped restraint plate is symmetrically welded on both sides of the starting point of the slit, and the inflection point of the U-shaped restraint plate is provided with a chamfer, and the diameter of the chamfer is 2 - 3 mm; (3) Use a laser to perform laser cladding on the metal powder along the slit to form a continuous cladding layer; (4) Measure the crack length on the surface of the cladding layer and the total length of the cladding layer, and calculate the crack rate; the calculation of the crack rate δ uses the following formula: Crack rate = Crack length / Total length of the cladding layer; (5) Complete the crack sensitivity evaluation according to the size of the crack rate.

2. The evaluation method for the crack sensitivity of laser cladding according to claim 1, wherein In step (1), the shape of the test plate is rectangular, the width of the test plate is 40 - 80 mm, the length of the test plate is 3 - 5 times the width, the thickness of the test plate is 3 - 20 mm, the length of the slit is 0.5 - 0.6 times the length of the test plate, the width of the slit is 0.5 - 1 mm, and the cleaning is carried out with acetone or alcohol.

3. The evaluation method for the crack sensitivity of laser cladding according to claim 1, characterized in that, In step (2), the welding of the U-shaped restraint plate uses tungsten inert gas welding, gas metal arc welding or shielded metal arc welding.

4. The evaluation method for the crack sensitivity of laser cladding according to claim 1, wherein In step (2), the welding sequence is to weld the cladding side first and then the non-cladding side.

5. The evaluation method for the crack sensitivity of laser cladding according to claim 1, wherein In step (3), the laser cladding starts from the starting end of the slit, clads along the slit, and the cladding length is 0.5 - 1.5 times the length of the slit.

6. The evaluation method for the laser cladding crack sensitivity according to claim 1, characterized in that, In step (3), the form of the laser cladding is single-pass cladding, the shielding gas used in the laser cladding process is argon or helium with a purity of 99.99%, the flow rate of the shielding gas is 15 - 20 L / min, and the shielding gas is supplied for 10 s before and after cladding.

7. The evaluation method for the crack sensitivity of laser cladding according to claim 1, wherein In step (3), the power of the laser during laser cladding is 1 - 3 kW, the scanning speed is 3 - 5 mm / s, and the rate of supplying metal powder is 10 - 30 g / min.

8. The evaluation method for the laser cladding crack sensitivity according to claim 1, characterized in that, In step (5), the crack sensitivity evaluation is: according to the size of the crack rate, evaluate the crack sensitivity of the same type of test plate under different metal powder types or different types of test plates under the same metal powder type. The higher the crack rate, the higher the crack sensitivity of the material under this condition to laser cladding.

Images